Non-Contact Optical Profilometry for Detection of Surface Changes of Hydroxyapatite Discs during Acid Attack

s Caries Res 2009;43:179–244 187 with MH were prepared by sectioning and polishing. Cross-sectional Vickers hardness of the 600  m thick enamel sections was measured across MH-affected and apparently sound areas and mean hardness values analysed by one-way ANOVA. Subsequently these sections were lapped to 100 m and assessed using polarizing microscopy (PM) and transverse microradiography (TMR). In specimens without post-eruptive breakdown (PEB) the visually sound surface layer was significantly harder (1.33–6.71 GPa) than the MH-affected enamel (0.07–6.14 GPa, p = 0.007). Specimens with PEB displayed a narrow ‘re’-mineralised surface layer of ̂ 5% increase in porosity from normal enamel when viewed by PM, representing 8% greater mineralisation than adjacent MH enamel measured using TMR. Hardnesses of MH enamel (0.07–6.14 GPa) were significantly lower (p ! 0.001) than sound enamel (2.55–8.92 GPa). MH hardness was variable as was the position within the enamel layer of the most severely affected area. The previously reported transition zone was present when lesions were assessed in an occlusal-cervical direction whereas changes in hardness occurred suddenly beneath the surface layer. The results demonstrate that changes in enamel physical characteristics associated with MH are significant. Surface characteristics, particularly in areas of PEB, suggest the capacity for increasing the mineralisation (and hence properties) of MH enamel clinically in a manner similar to that demonstrated for early caries lesions.